The present disclosure relates generally to methods for laying subsea pipelines. More specifically, in certain embodiments the present disclosure relates to methods of laying subsea pipelines comprising expansion loops and associated systems.
In the offshore oil and gas industry pipelines are frequently placed on the seafloor to connect wells to production platforms on the surface, or other structures on the seafloor. Typically, these pipelines are placed on the seafloor utilizing a pipe laying vessel.
Briefly, a pipe laying vessel is a specialized floating facility capable of deploying subsea pipelines from its deck to the sea floor. Examples of conventional pipe laying vessels and methods of laying subsea pipelines are described in U.S. Pat. Nos. 5,971,666, 5,836,719, and 3,438,213, European Patent No. 3,438,213, and U.S. Patent Application Publication Nos. 2014/0334880, 2014/0227039, 2012/0020739, and 2011/0274498, the entireties of which are hereby incorporated by reference.
As the temperatures and pressures of production fluids have become higher as higher pressure and higher temperature offshore wells are being developed, one of the major design challenges for subsea pipelines is the reduction and accommodation of the effect of these high pressures and temperatures on subsea pipelines. Subsea pipeline systems must be capable of accommodating growth of the pipelines due to expansion introduced by temperature and pressure. If this expansion is not accommodated then the pipelines may exceed their allowable limits of stress in the materials and, if the cyclic stress amplitudes are high enough in magnitude and number, potentially cause fatigue of the material. Another difficulty that must be addressed is the tendency of pipelines to “walk,” that is physically move, in response to this expansion, particularly if such expansion, or other loading, is asymmetric.
One current method to accommodate expansion of pipelines to mitigate the above problems is to provide expansion loops at several points along the extent of the pipeline. Expansion loops may be installed onto subsea pipelines after the subsea pipelines have been laid. The installation of these expansion loops may be a difficult process, since the loop needs to be inserted into the line after placement of the pipeline on the seafloor or made up before deploying the subsea pipeline. Each of the insertion methods requires the use of connection equipment, generally referred to as “connectors.” Conventional expansion loops require connectors at each end of the loop to connect them to the subsea pipelines. The seals of such connectors however may be subject to failure due to the movements of the subsea pipelines and other factors, such as aging, chemical attack and unexpected loading.
It is desirable to develop methods of laying subsea pipelines that comprise one or more expansion loops that do not require the use of connecters to join the subsea pipelines to the expansion loops. It is also desirable to develop a method of laying a continuous section of subsea pipeline that comprises one or more expansion loops.